Yellow Foxtail (Setaria pumila (=S. glauca)) is a monocot weed in the Poaceae family. In Ontario this weed first evolved resistance to Group C1/5 herbicides in 1981 and infests Corn (maize), and Cropland. Group C1/5 herbicides are known as Photosystem II inhibitors (Inhibition of photosynthesis at photosystem II). Research has shown that these particular biotypes are resistant to atrazine and they may be cross-resistant to other Group C1/5 herbicides.

The 'Group' letters/numbers that you see throughout this web site refer to the classification of herbicides by their site of action. To see a full list of herbicides and HRAC herbicide classifications click here.

Field, Greenhouse, and Laboratory trials comparing a known susceptible Yellow Foxtail biotype with this Yellow Foxtail biotype have been used to confirm resistance. For further information on the tests conducted please contact the local weed scientists that provided this information.

Genetics

Genetic studies on Group C1/5 resistant Yellow Foxtail have not been reported to the site. There may be a note below or an article discussing the genetics of this biotype in the Fact Sheets and Other Literature

Mechanism of Resistance

The mechanism of resistance for this biotype is either unknown or has not been entered in the database. If you know anything about the mechanism of resistance for this biotype then please update the database.

Relative Fitness

Triazine resistant weeds often exhibit a lower relative fitness when compared to susceptible biotypes. The most common mutation conferring triazine resistance (Ser 264 to Gly mutation of the psbA gene) also causes a reduction in CO2 fixation, quantum yield, and seed and biomass production. There is no record in this database referring specifically to fitness studies on Group C1/5 resistant Yellow Foxtail from Ontario.

The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in Ontario have been instrumental in providing you this information. Particular thanks is given to Clarence Swanton for providing detailed information.

The potential for future commercialization of glyphosate-resistant wheat necessitates evaluation of agronomic merits of this technology. Experiments were established to evaluate glyphosate-resistant wheat and weed responses to glyphosate rate, application timing, and tank mixtures. Glyphosate at 1680 g/ha did not injure wheat. Wheat response to glyphosate applied during the 1- to 3- or 3- to 5-leaf stage of the crop was not different from that of untreated wheat. Wheat was injured more from glyphosate applied in combination with thifensulfuron or dicamba than from individual herbicides at one of 6 locations, but grain yield was not affected by glyphosate tank mixtures. Glyphosate application timing did not affect the control of wild oat or common lambsquarters (Chenopodium album) 56 days after the treatment. Glyphosate, when applied during the 1- to 3-leaf stage of the crop provided better control of wild buckwheat (Fallopia convolvulus) than later glyphosate application, whereas glyphosate applied during the 3- to 5-leaf stage provided the best control of green foxtail (Setaria viridis), yellow foxtail (S. pumila), redroot pigweed (Amaranthus retroflexus), and Canada thistle (Cirsium arvense). Weed control with glyphosate tended to be better than conventional herbicides, and wheat treated with glyphosate produced approximately 10% more grain than wheat treated with conventional herbicide tank mixes..

Field studies were conducted at Clayton, Rocky Mount and Lewiston-Woodville, North Carolina, USA, in 2001 and 2002, to evaluate weed management, crop tolerance and yield in strip- and conventional-tillage glyphosate-resistant cotton. Cotton was treated with 2 glyphosate formulations, i.e. glyphosate-IP (isopropylamine salt) or glyphosate-TM (trimethylsulfonium salt) at early postemergence (EPOST) alone or in a mixture with S-metolachlor. Early season cotton injury was minimal (3%) with either glyphosate formulation alone or in mixture with S-metolachlor. Weed control and cotton yields were similar for both glyphosate formulations. The addition of S-metolachlor to either glyphosate formulation increased control of broadleaf signalgrass (Urochloa platyphylla), goosegrass (Eleusine indica), large crabgrass (Digitaria sanguinalis) and yellow foxtail (Setaria pumila) at 14 to 43% compared to the control by glyphosate alone. S-metolachlor was not beneficial for late-season control of entire leaf morningglory (Pharbitis hederacea), jimsonweed (Datura stramonium), pitted morningglory (Ipomoea lacunosa) or yellow nutsedge (Cyperus esculentus). The addition of S-metolachlor to either glyphosate formulation increased control of common lambsquarters (Chenopodium album), common ragweed (Ambrosia artemisiifolia), Palmer amaranth (Amaranthus palmeri), smooth pigweed (Amaranthus hybridus) and velvet leaf (Abutilon theophrasti) at 6 to 46%. The addition of a late postemergence-directed (LAYBY) treatment of prometryn plus MSMA increased control to greater than 95% for all weed species regardless of EPOST treatment, and control was similar with or without S-metolachlor EPOST. Cotton lint yield was increased 220 kg/ha with the addition of S-metolachlor to either glyphosate formulation compared to yield from glyphosate alone. The addition of the LAYBY treatment increased yields by 250 and 380 kg/ha for glyphosate plus S-metolachlor and glyphosate systems, respectively. S-metolachlor residual activity allowed for an extended window for more effective LAYBY application to smaller weed seedlings instead of weeds that were possibly larger and harder to control..

Studies were carried out in 1998-2001 in Michigan, USA, to determine the effect of glyphosate application timing and row spacing (38 and 76 cm for glyphosate-resistant maize hybrid DK 493RR and 19, 38 and 76 cm for soyabean cv. 92B71) on the yield of these crops. Glyphosate was applied when average weed canopy height reached 5, 10, 15, 23, and 30 cm. The weeds present in these studies included velvetleaf (Abutilon theophrasti), redroot pigweed (Amaranthus retroflexus), common ragweed (Ambrosia artemisiifolia), common lambsquarters (Chenopodium album), jimsonweed (Datura stramonium), barnyardgrass (Echinochloa crus-galli), fall panicum (Panicum dichotomiflorum), giant foxtail (Setaria faberi), yellow foxtail (Setaria glauca [S. pumila]), green foxtail (Setaria viridis), and eastern black nightshade (Solanum ptycanthum). Under highly competitive growing conditions (below normal rainfall and high weed density), maize yield was first reduced when weeds reached 10 and 15 cm in height with maize planted in 38- and 76-cm row widths, respectively. Under similar conditions, soyabean yield was first reduced when weeds reached 15 and 23 cm with soyabean planted in 19- and 38-cm row widths, respectively. Yield losses occurred only in the untreated control when soyabean was planted in 76-cm rows. When growing conditions were less competitive (adequate rainfall and lower weed density), yield losses occurred only when weeds reached 30 cm or more in maize and only in the untreated control in soyabean. Maize and soyabean yields were higher when planted in narrow rows in 3 of 4 years but were more susceptible to early-season weed interference than maize and soyabean in wide rows. Maize yield was affected more by weed interference than was soyabean yield. The product of weed height by weed density, as the independent variable, resulted in the best linear fit for both maize and soyabean yields. High weed densities increase the risk of yield loss and must be considered when determining the appropriate timing for total post-emergence herbicide applications such as glyphosate. Sequential glyphosate applications in maize did not increase yield..

Glyphosate-resistant maize hybrid DK 493RR and soyabean cv. 92B71 were planted in narrow- and wide-row spacings in East Lansing, Michigan, USA, during 1998-2001 to study the effects of glyphosate application timing and row spacing on light interception and subsequent weed growth. The weeds in the experimental area included Setaria faberi, S. viridis, S. glauca [S. pumila], Echinochloa crus-galli, Panicum dichotomiflorum, Chenopodium album, Amaranthus retroflexus and Abutilon theophrasti. Glyphosate was applied when weeds were 5, 10, 15, 23 and 30 cm in height. Maize planted in narrow rows (38 cm) had greater light interception than maize planted in wide rows (76 cm) from 35 to 55 days after crop emergence. Soyabean planted in narrow rows (both 19 and 38 cm) had greater light interception throughout the growing season than soyabean in 76-cm row. At maximum canopy closure, narrow-row (both 19 and 38 cm) soyabean intercepted more light than narrow-row maize. Biomass of weeds after glyphosate application was greater when soyabean was planted in 76-cm than in 19- or 38-cm rows. However, weed biomass was generally similar in both row spacings of maize. Sequential glyphosate applications reduced weed biomass in maize each year compared with a single glyphosate application at the 5-cm weed height. Sequential glyphosate applications that followed initial glyphosate application to 10- or 15-cm tall weeds did not reduce weed biomass compared with a single application..

The effects of atrazine and other triazine herbicides were compared on two biotypes of Setaria faberi and S. viridis that were not controlled by atrazine in maize fields in Spain. S. faberi and S. viridis biotypes from treated maize fields had no significant inhibition of photosynthetic activity following incubation with atrazine (100 µM). The R biotypes of S. faberi and S. viridis were 10.0 and 6.96 times less sensitive to atrazine than the S biotypes, respectively. Results from ED50, absorption and translocation, and fast fluorescence assays showed that S. faberi and S. viridis could have 2 mechanisms of resistance: a detoxification mechanism and a target site mutation in the R biotypes of both species. Hill reaction assays suggested that resistance was due to a mutation in the D1 protein. R and S biotypes detoxified atrazine to a similar extent, but R biotypes metabolized atrazine to conjugate atrazine faster than the S biotypes. Atrazine metabolism analysis was carried out with 5 species of Setaria. The hierarchy of tolerance level to atrazine was: S. verticillata = S. adherens [?S. adhaerens = S. verticilliata] > S. faberi = S. viridis >> S. glauca [S. pumila]. The R biotypes of S. faberi and S. viridis were cross-resistant to all the triazine herbicides used..